RDW

Understanding the marker

RDW describes how much red blood cells vary in size. It is read with average cell size and haemoglobin to understand the blood-count pattern.

RDW describes variation in red cell size. It can support the assessment of anaemia when interpreted with Hb, MCV and iron or vitamin tests; it cannot identify a deficiency on its own.

What does high RDW mean?

High RDW means there is more variation in red-cell size. Haemoglobin, MCV and relevant iron or vitamin tests help explain why. RDW alone does not identify a nutrient deficiency.

What does low RDW mean?

Low RDW means the red cells have relatively similar sizes. This finding alone is usually of limited significance, but the other blood-count results still need to be considered.